1. Field of the Invention
Aspects of the present invention relates to a printed circuit board assembly, and more particularly, to a printed circuit board assembly enhancing the ability of transmitting a signal.
2. Description of the Related Art
Generally, a printed circuit board assembly includes a printed circuit board provided to an electric home appliance such as a digital TV, a computer or the like, and an advanced communication device, etc. The printed circuit board assembly is manufactured by forming a plurality of signal lines on a predetermined substrate, mounting a plurality of surface mounted devices (SMDs), and electrically connecting the signal lines therewith. Examples of the SMDs include an integrated circuit, a resistor, a connector, a capacitor or the like. The substrate is formed of a rigid material (such as epoxy resin, phenolic resin or the like) or a flexible material (such as polyimide or the like). The printed circuit board assembly may include multiple layers. The SMDs are mounted on the printed circuit board assembly by soldering, ball grid, pin or other mounting mechanisms.
FIG. 1A is a perspective view illustrating a conventional printed circuit board assembly. As shown in FIG. 1A, a conventional printed circuit board assembly includes a substrate 100, a signal line 111 formed on the substrate 100, an SMD 115 mounted on the substrate 100, and a pad 113 for mounting the SMD 115 on the substrate 100 to electrically connect the SMD 115 with the signal line 111. Here, the signal line 111 maintains an impedance of 50 ohm to prevent signal distortion. For example, in the case that a dielectric (not shown) forming the substrate 100 has a height of 0.1 mm, the signal line 111 has a width of approximately 0.18 mm. However, because of the size of the SMD 115, the pad 113 should have a relatively big width of 1.5 mm to electrically connect the SMD 115 with the signal line 111.
FIG. 1B is an equivalent circuit diagram of the conventional printed circuit board assembly. As shown in FIG. 1B, parasitic capacitance 131 refers to the parasitic capacitance which the pad 113 has to electrically connect the SMD 115 with the signal line 111 by soldering or the like. Capacitance 133 refers to the capacitance which the SMD 115 such as a capacitor has. A solid line arrow refers to a signal transmission direction, and a broken line arrow refers to a signal reflection direction.
In the conventional printed circuit board assembly shown in FIG. 1A, since the width of the pad 113 is bigger than that of the signal line 111, the parasitic capacitance 131 may be caused when a signal is transmitted from a transmitting terminal 120 to a receiving terminal 121. The parasitic capacitance 131 causes an impedance nonconformity of the signal line 111, and causes noise in the transmitting terminal 120, thereby complicating configuration and increasing cost. Also, the reflected signal causes noises in an adjacent signal line, and causes an electromagnetic interference (EMI). Especially, in the case that a high frequency signal is transmitted through the signal line 111, the parasitic capacitance 131 may cause a serious impedance nonconformity.